Total internal reflection light modulating microstructure devices

ABSTRACT

A light modulating switch ( 210 ) including a switching element ( 218 ) having a first portion ( 226 ) of electro-optic material to which first and second electrodes ( 213, 224 ) are associated. A second portion ( 228 ) is composed of material having an index of refraction matching that of the first portion ( 226 ) when no voltage is applied to electro-optically activate the first portion ( 226 ), but the index of refraction of the second portion ( 228 ) is less than the index of refraction of the first portion ( 226 ) when the first portion ( 226 ) is electro-optically activated by application of voltage to the electrodes ( 213, 224 ). The first and second portions ( 226, 228 ) are in close conjunction with each other such that a TIR boundary ( 230 ) is formed at the junction of the first and second portions ( 226, 228 ) and the switching element ( 218 ) is oriented with respect to at least one incident light beam ( 240 ) such that the incident light beam ( 240 ) enters the first portion ( 226 ) and strikes the boundary ( 230 ) at an angle such that the light beam ( 240 ) is totally reflected internally when the first portion ( 226 ) is electro-optically activated, but which will pass unreflected through the boundary ( 230 ) when the first portion ( 226 ) is not electro-optically activated. The thickness of the second portion ( 228 ) is preferably reduced by removal of a step region ( 246 ) so that electric field lines within the active first portion ( 226 ) are more narrowly directed and the TIR boundary ( 230 ) is flatter and more regular.

This application is a continuation of patent application Ser. No.09/434,085, filed Nov. 5, 1999, now U.S. Pat. No. 6,381,060, which is acontinuation-in-part of patent application Ser. No. 08/959,778, filed onOct. 29, 1997, now U.S. Pat. No. 6,310,712.

TECHNICAL FIELD

The present invention relates generally to light modulators and lightswitches, and more particularly to electro-optic modulators. Theinventor anticipates that primary application of the present inventionwill be in high-speed signal processing and it may also be used inoptical interconnects, telecommunications and flat panel displays.

BACKGROUND ART

Electro-optic modulators have been well known in the art for years, butfor multi-channel applications they have suffered from severaldisadvantages. Prior art modulator arrays have usually been formed fromsingle wafers of electro-optically active material onto which surfaceelectrodes have been attached, to form channels which are defined by theelectric field lines within the optical wafer. Cross-talk, orinterference between channels, has been a problem because electro-opticmodulators are vulnerable on at least two levels. Since the channels arenot restricted except by the electric field lines, activity in onechannel can easily induce electro-optic interference in a nearbychannel. This is in addition to usual electrical cross-talk experiencedby closely grouped and unshielded electrical contacts. Also, previouselectro-optic modulators and light switches have often relied on surfacedeposited electrodes, which produce electric field lines that arefringed, rather than channeled and directed. Due to the exponentialdecay of the electric field intensity inside the material, very highvoltages may be required to drive the material to produce the desiredelectro-optic effect.

Electro-optic materials, such as LiNbO₃, can be expensive, and canrequire high driving voltages. Liquid crystal modulators have also beenused, but response times for this type are typically very slow, on theorder of milliseconds. Also, the electro-optic effect exhibited by amaterial can be of several different orders, depending on the material.A first order effect, called the Pockels effect, is linear in itsresponse to increase in applied voltage. A second order effect, calledthe Kerr effect, is quadratic in its response, thus a greater increasein effect can be produced relative to an increase in voltage. This cantheoretically allow smaller driving voltages in a primarily Kerr effectmaterial to be applied to produce a comparable electro-optic effectcompared to material which produces primarily Pockels effect.

Lead zirconate titanate polycrystalline ceramic which is doped withlanthanum (PLZT) is a relatively inexpensive, optically transparentceramic which can be made to exhibit either the quadratic Kerr effect orthe linear Pockels effect, depending on the composition, and can beformed into wafers easily and used in sol-gel moldings. The concentrateof lanthanum, or “doping”, is variable, and can lead to varyingcharacteristics in the material. PLZT that is commercially available istypically made from a “recipe” which produces a very high dielectricconstant κ. Very high κ values produce high capacitance values C, whichin turn produce high power requirements, as power (P) is proportional toCV²/2 where V=voltage. High power consumption in turn generates heat, sothat some modulators that require high voltage also may require cooling.If the proportion of lanthanum dopant, or other components, in thematerial is adjusted, the dielectric constant value and electro-opticconstant value, as well as the type of electro-optic effect (Kerr orPockels), may also be varied, with the result affecting capacitance andpower consumption.

Prior art inventions for modulating light in arrays generally sufferfrom common problems experienced by multi-channel optical and electricalsystems in which the channels are not appropriately isolated. Asdiscussed above, interference is easily induced in nearby channelsresulting in cross-talk which can distort image clarity and corrupt datatransmissions. Additionally, much of the prior art requires high drivingvoltages that are incompatible with TTL level power supplies.

U.S. Pat. No. 4,746,942 by Moulin shows a wafer of PLZT electro-opticceramic material with a large number of surface mounted electrodes. Thisinvention suffers from the disadvantage of cross-talk between channels,although there is discussion of attempts to decrease cross-talk by useof large electrodes and increased space of the electro-optic windows.This results in less efficient use of the material. Although typicaldriving voltages are not given, with larger areas of material, higherapplied voltages become necessary to provide the necessary electricfield density in the wafer.

U.S. Pat. No. 4,867,543 by Bennion et al. describes a spatial lightmodulator made of a solid sheet layer of electro-optic material such asPLZT, which has paired surface electrodes. This has the disadvantage ofrequiring a driving voltage of approximately 20 volts to produce a phaseretardation of PI radians. U.S. Pat. No. 4,406,521 by Mir et al.discloses a panel of electro-optic material which uses electrodes todefine pixel regions. It speaks of using voltages in the range of100-200 volts. U.S. Pat. No. 5,033,814 by Brown et al. also shows asingle slab of electro-optic material which requires a driving voltageof 150 volts. U.S. Pat. No. 5,528,414 to Oakley discloses a single waferof Pockels crystal with surface mounted electrodes requiring a 70 voltdriving voltage. Besides being obviously incompatible with TTL voltagelevels, none of these inventions have any mechanism for confiningelectric field lines. Also, in general, use of higher driving voltageswill generate heat in the electro-optic material, which can mean that acooling system may be required.

U.S. Pat. No. 5,220,643 by Collings discusses an array of opticalmodulators which are built into a neural network. These modulators aremostly of liquid crystal type, although use of PLZT is mentioned. U.S.Pat. No. 4,560,994 by Sprague shows a single slab of electro-opticmaterial with an array of electrodes which create fringe electricfields, which are not channeled. Sarraf's U.S. Pat. No. 5,521,748 alsodiscloses a modulator array in which mirror-like devices deflect ordeform when electrostatic force is applied. U.S. Pat. No. 4,367,946 toVarner also discusses a light valve array, with one specificallypreferred material being PLZT. However, all four of these inventions canbe expected to have the same problems of cross-talk, which the presentinvention is designed to eliminate.

For the foregoing reasons, there is a need for an array of discretelight modulating elements which can operate at TTL voltage levels, andat high speeds, with almost no cross-talk, and which can be used toproduce small pixels or which can be grouped together to create largerpixels and large two dimensional panels or sheets.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide anarray of discrete modulated elements of electro-optic material.

Another object of the invention is to provide arrays ofelectro-optically modulators that can be driven by TTL voltages, andthus be compatible with standard TTL power supplies.

Yet another object of the invention is to produce arrays ofelectro-optic modulators which have very little cross-talk betweenchannels.

Still another object of the present invention is to provide an arraywith very fast response and switching time.

A further object of the present invention is to provide an array ofpixels which can be of very small dimensions to reduce problems ofaliasing in optical displays.

A yet further object of the present invention is to produce lightmodulating arrays that can be manufactured by conventional methods veryinexpensively.

Briefly, one preferred embodiment of the present invention is a lightmodulating including a switching element having a first portion ofelectro-optic material to which first and second electrodes areassociated. A second portion is composed of material having an index ofrefraction matching that of the first portion when no voltage is appliedto electro-optically activate the first portion but the index ofrefraction of the second portion is less than the index of refraction ofthe first portion when the first portion is electro-optically activatedby application of voltage to the electrodes. The first and secondportions are in close conjunction with each other such that a TIRboundary is formed at the junction of the first and second portions andthe switching element is oriented with respect to at least one incidentlight beam such that the incident light beam enters the first portionand strikes the boundary at an angle such that the light beam is totallyreflected internally when the first portion is electro-opticallyactivated, but which will pass unreflected through the boundary when thefirst portion is not electro-optically activated.

A second preferred embodiment uses an element in which the thickness ofthe second portion is reduced by removal of a step region so thatelectric field lines within the active first portion are more narrowlydirected and the TIR boundary is flatter and more regular. The stepregion is filled with a material having a low dielectric constant k.

A third preferred embodiment uses a number of optical switches in anarray or matrix to create N×N or N×M cross-connect switches.

An advantage of the present invention is that it may be operated withTTL voltages or lower.

Another advantage of the invention is that because of the low voltagerequirements, heating of the elements is reduced and requirements forcooling are minimized.

Yet another advantage of the present invention is that very smallelements may be produced, thus allowing for very fine image resolution.

A further advantage of the present invention is that cross-talk betweenchannels is nearly eliminated.

A still further advantage of the present invention is that standardmicro-machining operations can be used, allowing for inexpensivemanufacture.

A yet further advantage of the present invention is that sol-gelprocesses can be used to create arrays very inexpensively.

Still another advantage of the present invention is that the elementscan be very rapidly switched, with switching times on the order ofpico-seconds (10⁻¹² seconds).

Yet another advantage of the present invention is that sol-gel processescan be used to make displays which are both thin and flexible. Thesemolding processes can produce arrays with large numbers of elementsquickly and for very low cost.

These and other objects and advantages of the present invention willbecome clear to those skilled in the art in view of the description ofthe best presently known mode of carrying out the invention and theindustrial applicability of the preferred embodiment as described hereinand as illustrated in the several figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The purposes and advantages of the present invention will be apparentfrom the following detailed description in conjunction with the appendeddrawings in which:

FIG. 1 is a perspective view of a system for modulating and switchinglight beams which uses a light modulating array, showing the modulationof impinging light beams;

FIG. 2 is a perspective view of a modulator array, and electricalcircuit showing an alternative location for conductive pads;

FIG. 3 is a perspective view of a modulator array, and electricalcircuit showing the elements mounted on a substrate of differentmaterial;

FIG. 4 is a perspective view of a modulator array and electrical circuitin which electrodes have been attached to the top and bottom wafersurfaces;

FIG. 5 is a perspective view of a modulator array and electrical circuitshowing an alternate location for conductive pads;

FIG. 6 is a perspective view of an alternate embodiment of a modulatorarray and electrodes;

FIG. 7 is a perspective view of another alternative embodiment of amodulator array and electrodes;

FIG. 8 is a perspective view of system for modulating and switchinglight beams which uses a modulator array and beamsplitters to separatemodulated and unmodulated beams into different channels;

FIG. 9 is a plan view of a system for modulating and switching lightbeams, which shows a single element of a modulator array used as analternate mechanism for separating modulated and unmodulated beams intodifferent channels;

FIG. 10 is a perspective view of a system for modulating and switchinglight beams which shows a single element of a different version of amodulator array used as an alternate mechanism for separating modulatedand unmodulated beams into different channels;

FIG. 11 is a perspective view of a modulator array in which electrodeshave been placed so as to produce an electric field which is collinearwith the direction of light propagation;

FIG. 12 is a cross-sectional view of an embedded electrode array in asol-gel matrix of electro-optic material;

FIG. 13 is a front perspective view of a single optical switch of thepresent invention;

FIG. 14 is a front perspective view of the single optical switch of FIG.13, from which the upper electrode has been removed for easier viewing,the switch being in an inactive state;

FIG. 15 is a front perspective view of the single optical switch of FIG.13, from which the upper electrode has been removed for easier viewing,the switch being in an active state;

FIG. 16 is a front perspective view of an alternative embodiment of asingle optical switch of the present invention which has improvedflatness and uniformity of TIR boundary;

FIG. 17 is a front perspective view of an optical switch havingelectrodes placed on the side walls of the element.

FIG. 18 is a top plan view of an array of optical switches configured asa cross-connect switch in which two upper and lower input signals crossto exit from output channels; and

FIG. 19 is a top plan view of an array of optical switches configured asa cross-connect switch in which two upper and lower input signals exitfrom upper and lower output channels without crossing.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention is an array of lightmodulating and switching microstructure devices. The present inventionsolves many of the problems of the prior art by using lanthanum dopedlead zirconate titanate crystal (PLZT), which is an opticallytransparent ceramic that becomes birefringent when proper voltage isapplied. PLZT has a quadratic electro-optic response to voltage increasethus allowing lower driving voltages. In addition, the present inventionuses an optimized compositional “recipe” in which the proportion oflanthanum dopant and matrix elements has been designed to produce lowdielectric constant κ, higher electro-optic efficiency, and thus lowpower requirements. Additionally, the electro-optic elements are3-dimensional and of very small size, generally 10 μm-200 μm in thelight propagation direction, or much less, depending on the design. Thisallows production of very high-density electric fields in these elementsby using small voltages, including TTL levels of approximately 5 volts,and lower. This has advantages because power supplies that are alreadyset up for TTL level digital components can supply the electro-opticmodulators as well. Cross-talk has been nearly eliminated by the use ofgrooves or regions which are filled with air'or other dielectricmaterials. These physically separate at least a portion of the elements,thus directing and channeling electric field lines more closely. PLZT,as well as other electro-optic materials, also allows for pico-secondresponse time, thus theoretically allowing very high switchingfrequencies of 100 GHz and more.

The use of embedded electrodes produces more uniform electric fieldstrength in the elements. This allows a much lower driving voltage and amuch more predictable and controllable electric field.

The present invention is also useful when using standard recipeelectro-optic materials, in which the dielectric constant has not beenminimized, and also in a variety of other electro-optic materials besidePLZT. Electro-optic materials fall generally into five categories, 1)electro-optic crystals, 2) polycrystalline electro-optic ceramics, 3)electro-optically active polymers, 4) electro-optic semiconductors, and5) electro-optic glasses. Although the electro-optic properties of thematerials are variable depending on composition, the present inventioncan be implemented with materials of any of these three categories.Specific examples of electro-optic materials besides PLZT which may beused include, but are not limited to, LiNbO₃, LiTaO₃, BSN, PBN, KTN,KDP, KD*P, KTP, BaTiO₃, Ba₂NaNb₅O₁₅, GaAs, InP, CdS, AgGaS₂, and ZnGeP₂.The very small dimensions of the elements result in very low elementcapacitance even when using material having a relatively largedielectric constant κ.

As illustrated in the various drawings herein, and particularly in theview of FIG. 1, a form of this preferred embodiment of the inventivedevice is depicted by the general reference character 10.

FIG. 1 illustrates an array of light modulating microstructures 10 aswell as a system 11 for modulating or switching light in a number ofindependent channels. In this preferred embodiment, the array 10 isformed from a wafer 12 of PLZT. PLZT has been chosen for its largeelectro-optic effect and low absorption for thin wafers.

If PLZT is used, the relative proportion of the Lanthanum dopant in theceramic can be very important in determining the driving voltagerequired for the elements. The composition also is important inestablishing the optical properties such as transparency, grain size andpore size, speed, power dissipation, operating temperature and formaximizing both the linear and the quadratic electro-optic coefficientsof the material. Commercial recipes for PLZT have largely used Lanthanumconcentrations of 9.0% to 12%. If Lanthanum concentration is varied inthe range of 8.5% to 9.0% of the PLZT ceramic and the concentration ofZirconium and Titanium are unchanged from typical ratios of 65/35, itmay be possible to achieve a higher quadratic electro-optic coefficient(R) in the PLZT for the La dopant percentage closer to 8.5%. For thePLZT compositions, where Zr and Ti are maintained in a 65/35 ratio andthe overall percentage of La is varied:

La=9.5%, R=1.5×10⁻¹⁶ m²/V²;

La=9.0%, R=3.8×10⁻¹⁶ m²/V².

It is known that for La<8.0%, PLZT loses quadratic electro-opticproperties. It is therefore expected that somewhere around 8.5% La thereshould be a maximum for R around (5-40)×10⁻¹⁶ m²/V².

This enhanced value of electro-optic coefficient provides manyadvantages. It will permit lower required driving voltages, and thuslower power dissipation in the material and hence lower heating of thedevice. This in turn allows the device to be driven at significantlyhigher frequencies, even without external cooling. Also, the use oflower La concentrations (which is a free electron donor) will result ina reduced “charge screening” effect. The overall result is highermodulation efficiency of devices manufactured from this material.

The wafer 12 has regions or grooves 14 formed to produce protrusions 16from the original thickness 18 of the wafer 12. The grooves 14 may beformed by any number of means, such as mechanical machining withmicro-saws, chemical etching using photo-resist masks, or laserablation, or the array may be molded in shape from polycrystallineceramic, among other methods. The grooves 14 provide isolation betweenthe channels of the array 10, serve to direct and channel the electricfield lines in the electro-optic material and thus allow the array tooperate with nearly zero cross-talk.

Each protrusion 16 has a top face 20, a first side face 22 and a secondside face 24, a front face 26 and a rear face 28. The grooves 14 can becut through the entire original thickness 18 of the wafer 12, in whichcase, the protrusions will have an independent bottom face 30, or if thegroove is not cut through the entire original thickness 18, the bottomface 30 will be integral with the wafer 12, as shown by the dotted linein FIG. 1.

The faces of the wafer 32 can be polished either before or after thegrooves 14 are formed, to prevent scattering of light entering orleaving the wafer 12. Electrodes 34 are attached to the protrusions 16by any of a number of ways, but one preferred method is to embed theelectrodes 34, as this may produce a more uniform electrical field. Itis also possible that the material of the electrode 34 may completelyfill the grooves 14. Conductive pads 36 of gold or some other metal orconductive material are used to attach electrical leads 38 to theelectrodes 34, which connect them in turn to the electrical power supply40. An electrical field is thus established which is oriented in atransverse direction relative to the direction of the incoming lightbeams 42. The width of electro-optic material between the grooves 14 inthe protrusions 16 establishes the electrode gap 44 in thisconfiguration of electrode 34 placement.

For ease of reference, an assembly containing a protrusion 16, attachedelectrodes 34, and conductive pads 36 shall be referred to as an“element”. The size of the wafer 12, the protrusions 16 and theelectrode gaps 44 will depend on the material chosen, and the desiredrange of applied voltages to be used. The electro-optic effect exhibitedby an element of a particular material depends on the electric fieldstrength within that element. The density of that field will in turndepend on the amount of applied voltage, the material chosen, and thephysical dimensions of the element in which the electric field iscontained. Using very small elements allows a large concentration ofelectric field density by use of small to moderate voltages. In thepresent invention, in order to use voltages in the TTL a range, around5V, it is estimated that the physical size of the elements, if made ofPLZT, will be on the order of 20 μm×20 μm×200 μm. The grooves 14 can bemade very small, and indeed may be limited by the size of machiningtools used to form them. Excellent results in terms of near zerocross-talk have been achieved using micro-sawing methods where the kerfsize of the saw cuts are around 25 μm. Effective reduction of cross-talkbetween channels may be achieved with grooves as small as 5 μm.

Such tiny elements can produce modulated beams of very small size,producing such fine image resolution that the unaided eye is incapableof distinguishing it. It may have applications where microscopic imagesare required, or where multiple beams are combined in groups of 5 or 10elements to make up 1 pixel in a display device.

The size of the elements will also depend on whether the beam istransmitted through the element or reflected from a rear surface, inwhich case, the length or the driving voltage can be cut roughly in halfto produce the same degree of modulation. Materials with smallerelectro-optic properties may require greater size or increased appliedvoltage to achieve proper modulation results.

In FIG. 1, a first element 46 and a second element 48 are shown, whichin this preferred embodiment, will be assumed to be composed of PLZT.Between the first element 46 and the voltage supply line, an open switch50 is shown to represent that the element 46 has no voltage applied, andis in an inactive state. It is, of course, to be understood that nothingso primitive as throw-switches need be used to practice the invention.Most likely, very high frequency (perhaps as much as 100 GHz or more)square waves of appropriate voltage will be used, but throw-switches areused here as an easy means of illustrating the state of the appliedvoltage.

The incoming light beams 42 having incoming linear polarization 54 whichis aligned with the upper tip 45 degrees to the left of vertical, (whichshall be referred to as “R” polarization) impinge on both elements 46and 48. This incoming light may be linearly polarized laser light, or itmay be initially unpolarized light, perhaps even including light from anincandescent bulb, which has been transmitted through a polarizer toproduce linearly polarized light. First element 46 is inactive, thus theoutgoing polarization 56 of the first element 46 is unchanged. It passesthrough an R aligned polarizer 60 and is detected by a light sensor orphoto detector 62, perhaps to be recognized as a digital “1”.

In contrast, switch 52 is closed leading to the second element 48, thusthe supply voltage is applied and the element 48 is active. The element48 becomes birefringent under the influence of the applied electricfield. Birefringence causes an incoming beam 42 which is linearlypolarized at a 45 degree angle relative to the direction of the appliedelectric field to split into two orthogonal components which arerespectively parallel and perpendicular to the electric field lines.These components travel along the same path but at different velocities.The electro-optic effect thus will cause a phase shift between the twocomponents, as one is retarded in relation to the other. After travelingthrough the element 48, the components re-combine with the result thatthe polarization of the emergent beam 58 is changed. If the voltage issufficient to cause a λ/2 shift in polarization, the polarization willbe rotated by 90 degrees, relative to its original orientation. In FIG.1, it is assumed that a λ/2 voltage of 5 volts has been applied whichproduces a 90 degree phase shift to give a linearly polarized outputbeam 58, which is oriented with the upper tip now 45 degrees to theright of vertical (which shall be referred to as “S” polarization). ThisS polarized light is now blocked by the R aligned polarizer 60, whichallows no light to reach the detector 62. This may be recognized by adigital device as a “0”.

If the applied voltage causes a λ/4 rotation, the outgoing polarization58 will be made into circular polarization, as the tip of the resultantelectric field vector will describe a circle as it propagates.Intermediate voltage values will result in elliptical polarization.These will be incompletely blocked by the polarizer 60, which will allowonly the R aligned component to pass. Thus, the light seen by thedetector 62 may be theoretically controlled anywhere in the range fromundiminished incoming intensity to total extinction, to produceanalog-type output signals if the appropriate control voltage isapplied.

FIG. 2 illustrates a different version of the modulator array 10. Awafer 12 is shown with attached or embedded electrodes 34, and in thisembodiment, the conductive pads 36 are located in a differentconfiguration for attachment to electrical leads 38.

FIG. 3 illustrates another version of the modulator array 10, in whichthe grooves 14 have been extended completely through the originalthickness 18 of the wafer. The elements 64 here are composed of theprotrusion 16 portions of the wafer 12 and their respective attached orembedded electrodes 22 and conductive pads 24 (see FIG. 1). A number ofelements 64 have been formed on a substrate 66 made from a differentmaterial which the bottom faces 30 now contact. This substrate 66 ispreferably a low dielectric material that is not electro-opticallyactive, such as SiO₂, for one example among many. The protrusions 16 maybe attached or glued to the substrate 66 prior to machining orattachment of the electrodes 34 and pads 36, or the completed elements64 may be assembled prior to attachment to the substrate 66.

FIG. 4 shows yet another version of the modulator array 10. In thisembodiment, electrodes 34 are attached to the top faces 20 of theprotrusions 16 and a single large electrode 68 is positioned on thebottom side 70 of the wafer 12. It is to be understood that a pluralityof appropriately placed individual electrodes could be used on thebottom side 70 of the wafer 12 in place of the single large electrode 68pictured here and in the following FIG. 5. Conducting pads 36 areattached to the top and bottom electrodes 34, 68 as attachment pointsfor the electrical leads 38. Polished front faces 26 are indicated asbefore, and incoming light beams 42 are shown to indicate orientation.The polarization direction has not been shown, as the principles ofphase retardation operate much the same as in FIG. 1, with a λ/2 shiftproducing a 90 degree rotation, etc. This placement of electrodes 34, 68produces a different orientation of transverse electrical fields, butstill retains the advantage of channel separation and minimization ofcross-talk which was unavailable in the prior art.

FIG. 5 shows a variation of the configuration in FIG. 4, in which theupper conductive pads 36 are located in a different orientation relativeto the wafer 12. The top and bottom electrodes 34, 68 are positioned asin FIG. 4, to produce a transverse electric field. The polished frontfaces 26 and incoming light beams 42 are again shown for orientationpurposes.

Although not pictured here, it is to be understood that this arrangementof top and bottom electrodes and the variations in conductive padlocations seen in FIGS. 4 and 5 can be used with elements which havebeen positioned on a different substrate material, in the mannersuggested by FIG. 3, if the substrate material has the proper conductiveproperties. It may also be possible for elements to be directly attachedto a single large bottom electrode which can act as a substrate tosupport and position the elements. Alternately, the electrodes may beattached or embedded on both sides of the electro-optic materialdirectly before mounting the assembled elements onto a substrate.

FIG. 6 shows another version of an array 10 of modified protrusions 72which have either been formed on the original wafer 12 or formedseparately on a substrate of different optically transparent material 66in a similar manner to the embodiment shown in FIG. 3. The modifiedprotrusions 72 are shown to be oriented with their long sides parallelto the long edge of the wafer 12 or substrate 66, but it should beunderstood that they may also be oriented with the long sides of theprotrusions 72 transverse to the long edge of the wafer 12 or substrate66. An incoming polarized light beam 42 enters from the bottom side 70of the wafer 12 or substrate 66 and is internally reflected on theangled first side face 74 and angled second side face 76 to reemergefrom the bottom side 70 of the wafer 12. If appropriate voltage has beenapplied to the electrodes 78, the resulting polarization of the emergentlight beam 80 will be modulated in the manner described above. Theangles of the faces here are chosen to allow total internal reflection,but it is to be understood that if a reflective coating is applied tothe faces, a variety of other angles may be used as well.

FIG. 7 illustrates yet another version of a modulator array 10 in whichthe protrusions 82 have been modified in another manner such that theangled second side face 84 of each has been angled to direct theemergent beam 86 out of the top face 20 of each protrusion 82. As inFIG. 6, the protrusions may be oriented in a transverse direction, adifferent substrate material may be used, and a reflective coating maybe applied to reflecting faces.

FIG. 8 shows a system 11 for modulating or switching light beams whichuses the modulator array 10 in much the same configuration as in FIG. 1.An incoming linearly polarized beam 42 of polarization “R” enters afirst element 46 which is inactive due to an open switch 50, so that itsexiting polarization 56 is unchanged. This enters a beamsplitter 88 thathas been positioned so that light of R polarization will be reflectedout of the beamsplitter at angle φ, as shown by reflected beam 90. In asecond element 48, which is active, the voltage is assumed to be such asto produce a λ/2 shift, the polarization is rotated 90 degrees to “S”orientation, and this passes through the beamsplitter 88, as shown byunreflected beam 92. These beams can be used to carry separate digitalinformation, and may be designated “channel 1” 94 and “channel 2” 96. Itis to be understood that beamsplitters can be used as a channelseparation device with any of the various embodiments illustratedherein.

FIG. 9 shows a top plan view of another system 11 for modulating orswitching light beams which uses a different version of a lightmodulating array 10. A single protrusion 16 is shown, which is composedof a first block 98 or portion of material having an index of refractionN₁, and a second block 100 of material having index of refraction N₂. Aboundary 102 is formed at the junction of the two materials. One of thetwo blocks, in this case the first block 98, has top and bottomelectrodes 104. First block 98 is composed of electro-optic materialsuch that when electrodes 104 are uncharged, the electro-optic materialis inactive, and N₁=N₂. When voltage is applied to electrodes 104, thefirst block 98 becomes active and the index of refraction changes forpolarization components which are aligned with the electric field linesso that for this polarization, N₁>N₂. When first block 98 is inactive,an incoming beam 106 is projected into the first block 98 at entry angleε to a normal such that the beam passes through the boundary between thetwo blocks 98, 100 and emerges as unreflected light ray 108. When firstblock 98 is active the index of refraction is increased such that totalinternal reflectance (TIR) occurs, and the beam is reflected back intothe first block 98 at the boundary 102, and emerges as reflected lightray 110. The two emergent beams 108 and 110 are separated by angle δ,which has been greatly exaggerated here. These separated beams 108, 110,can be detected by sensors 112, and thus be used to establish channelseparation for data transmission.

Alternatively, the protrusion 16 can be made from a single integralblock of material, which has been electro-optically divided intoportions or sections. A first section 98 may have electrodes 104attached to induce a different index of refraction in this section. Anincoming beam 106 will then be totally internally reflected, asdescribed above, at the interface between the activated 98 andunactivated sections 100. This interface or boundary 102 can beestablished more definitely by having the second section 100, be of adifferent thickness than the first 98. This serves to direct theelectric field lines better so that less fringing is produced, and asharper interface boundary 102 is established.

FIG. 10 shows a perspective view of another system 11 for modulating orswitching light beams which uses yet another version of the lightmodulating array 10 to perform channel separation. A single prism-shapedprotrusion 114 is shown, which can be electro-optically activated byelectrodes 116 to increase the index of refraction. This causes thelight beam to be bent towards the normal upon entry slightly differentlythan when the material is an inactive state. Thus when the element isactive, the light beam will follow a first path 118, and will emerge ata slightly different angle relative to the normal upon leaving theelement, thus following a first exiting path 120. In contrast, when theelement is inactive, the light follows a second path 122 upon entry, andfollows a second exiting path 124. Both of these second paths are shownin dashed line in FIG. 10. These first and second exiting paths 120, 124are separated by angle β, and they can be further directed by mirroredsurfaces 126 to sensors 128 to produce separate channels. The separationof the paths and the separation angle has been exaggerated in the FIG.10.

FIG. 11 illustrates yet another version of the present light modulatingarray 10 in which end-mounted electrodes 130 each having an aperture 132have been attached to the front faces 26 and rear faces 28 of theprotrusions 16. In this configuration, the electric field lines arecollinear with the direction of incoming light beams 42. The applicationof appropriate applied voltage results in the change in polarized outputin a manner similar to that discussed above. It is to be understood thatthe above mentioned methods of splitting the output into separatechannels, or using an external polarizer and sensor may be used, as wellas mounting of elements on different substrate material, and variationsin conductive pad placement.

It is also possible to have a light-producing element, such as a diodelaser, with a modulating element physically attached at the laser'soutput, in order to produce a single integrated element.

Another variation of the preferred embodiment uses sol-gel processing tocreate an array of elements that are fixed in a flexible medium. Sol-gelprocessing is a chemically based, relatively low temperature (400-800degrees C.) method that can produce ceramics and glasses with betterpurity and homogeneity than higher temperature (2,000 degrees C.)conventional processes.

When using molding processes, two approaches are possible. In the firstapproach, a non electro-optic, optically transparent or non-transparentmatrix is prepared. Electrodes are deposited on the side walls. Then itis filled with soft, curable electro-optic material of sol-gel type orpolymer resin. It is then cured to produce an array of electro-opticmodulators separated spatially by non electro-optic material.

In the second approach, an electro-optically active matrix of solid orflexible material is prepared. Electrodes are deposited on the sidewalls. Then it is filled with soft, curable non electro-optic material,of optically transparent or non transparent, sol gel type or polymerresin. Then it is cured to produce an array of electro-optic modulatorsseparated spatially by non electro-optic material.

For the PLZT thin films made by the sol-gel process with 1-2 μm spacingbetween embedded adjacent electrodes, λ/2 voltages range from 20-30Volts for 0.5 μm thick films, to TTL levels (4-5 Volts) for 1-2 μm filmthickness. This idea is very attractive for large area flat paneldisplay applications, which function like CRT tubes and which maysuccessfully compete with them. Because electrode spacing is necessarilyvery small to achieve low driving voltages, resulting pixel size is alsovery small, which makes this embodiment ideal for high-resolution flatpanel displays or spatial light modulators. This fine pixel structure isbelow typical resolution capability of the human eye, so for consumerapplications, sub-micron and micron size substructures may be aggregatedto produce standard sized pixels (usually dozens or hundreds ofmicrons). To simplify the manufacturing process and make it compatiblewith existing flat panel technology, the pixel size can be made larger.In this case, each pixel represents an interdigital pattern of PLZTembedded shutter electrodes.

FIG. 12 shows a top plan view of a modulator array 10 composed ofembedded electrodes 134 that are contained in a sol-gel matrix 136. Thearrow lines indicate electric field lines 138. The height of theelectrodes 134 (out of drawing plane) is defined by the thickness of thefilm. In the figure, light also travels perpendicular to the drawingplane. For non-polarized light, the modulator array 10 is placed inbetween two cross polarizers (not shown).

The electrode structures can be deposited either prior to the sol-gelfilm deposition, or after it, using standard etching or micro-machiningtechniques. Using etching techniques and molding processes, the heightof the electrodes 134 can be much higher, 10 μm or more with the same1-2 μm spacing between electrodes. In this case, sol-gel can fill thespacings between electrodes 134 and the thin film can still be thinenough (a few microns) to guarantee the same fabrication process andsimilar process conditions. This will allow driving or switchingvoltages on the TTL level (4-5 Volts) or below (1-3 Volts and evenlower). The arrays thus fabricated can be used in either transmissive orreflective modes. Additionally, the sol-gel material can either be usedto completely fill the gap between electrodes, or it can instead bedeposited on the sides of the electrodes as a coating. If used as acoating, an additional electrode can be added on the outer side of thesol-gel coating to make a complete element, each element being separatedfrom its neighbor by a gap or groove.

FIG. 13 shows a preferred embodiment which makes use of several of theinventive features previously disclosed. An optical switch 210 is shownwhich makes use of total internal reflection at the boundary between anactivated portion and an inactive portion of electro-optic material, inthe manner of the embodiment previously described and shown in FIG. 9.

The optical switch 210 is fabricated upon a substrate of semi-conductormaterial 212, which acts as a first electrode 213. Upon this substrate,a matrix of material 214, preferably glass is formed. Light conductivechannels 216 are formed in the matrix, and these channels can be formedof either fiber optic material, or preferable are waveguides. Theswitching element 218 is preferably formed by making a cavity 220 in thematrix material 214, which is then filled with electro-optic material222. In the preferred embodiment, this electro-optic material is PLZTwhich is introduced in a sol-gel state, and then cured to a solid. ThePLZT sol-gel is used to fill the cavity, and then after hardening, asecond electrode 224 is placed on top of a first portion 226 of theelectro-optic material 222, leaving a second portion 228 which is notcovered by the second electrode 224. The second electrode 224 isconnected to a high-speed switching power supply (not shown). At theboundary between the first portion 226 and the second portion 228, thereis a potential total internal reflection (TIR) boundary 230. Thisboundary will act to reflect incident light which approaches from anangle greater than the critical angle for the interface of materialswith different indices of refraction. For TIR to occur, the incidentlight beam must also have polarization which is parallel to the plane ofthe boundary. In FIG. 13, this would be vertical polarization.

The first material portion 226 and second material portion 228, asdiscussed above, may be portions of a single unity piece ofelectro-optic material. It is also possible that the two portions 226,228 are separate components, perhaps composed of different materials,which have indices of refraction which match closely enough that lightwill not be reflected at the boundary 230 when the first portion 226 isinactive, but which will be totally reflected internally when the switch210 is active.

Of the four light conductive channels 216 shown, going counter-clockwisefrom the upper left hand channel, there is a first incoming signalchannel 232 and a second incoming signal channel 234, a first outgoingsignal channel 236, and a second outgoing signal channel 238.

FIG. 14 illustrates an optical switch 210 from which the secondelectrode 224 has been removed for easier viewing. The optical switch210 shown is in an inactive state, i.e. no voltage is applied to theelectrodes, thus the index of refraction of the first portion 226 of thePLZT and the second portion 228 exactly match. Therefore, the TIRboundary 230 only potentially exists, and is shown in dashed lines inthe figure. A first incoming signal 240 is shown as a black arrow whichenters the switching element 218 through the first incoming signalchannel 232. As the switch 210 is inactive, the first incoming signal240 continues unaffected and is relayed through the first outgoingsignal channel 236. A second incoming signal 242 is depicted as a whitearrow which enters from the second incoming signal channel 234, and alsocontinues in a straight line to exit from the second outgoing signalchannel 238. Since the second incoming signal is not intended to bemodulated by the TIR boundary 230, it is merely relayed onward from thisswitch 210. The second incoming signal channel 242 together with thesecond outgoing signal channel 238 can be thought of as a passivecrossing channel 239 with respect to the second incoming signal 242. Theincorporation of a passive crossing channel 239 is useful in routing ofsignals in larger arrays of optical switches, as will be describedbelow, but is not necessary to the operation of the individual switch210 shown in FIG. 14. Its inclusion here is thus not to be construed asa limitation on the structure or operation of the switch 210.

FIG. 15 illustrates the optical switch 210, again with the top electroderemoved, in an active state. Thus, the electrodes, although not shown,are charged and an electric field is generated in the first portion 226of electro-optic material. The index of refraction is thus increased forthis portion, so that total internal reflection is produced for lightwhich approaches at the angle assumed by the first incoming signal 240,again shown as a black arrow. The TIR boundary 230 is established, andthe first incoming signal 240 is reflected off the TIR boundary 230 andinto the second outgoing signal channel 238 as the reflected beam 244.Thus the first incoming signal can be switched from the first outgoingsignal channel 236 whenever the appropriate electric field is generatedin the first material portion 226. This switching can be done veryquickly, on the order of pico-seconds (10⁻¹² seconds), and as explainedabove, standard TTL voltages can be used, which are compatible with manystandard power supplies.

The quality of the reflected beam 244 is dependent on the flatness anduniformity of the TIR boundary 230, much the same as that of anyreflecting surface. A reflected beam from a very flat surface willnaturally tend to retain the properties of the incident beam better thana reflected beam from a less flat and less uniform surface. Theproperties of the boundary of the electric field produced define theflatness of the TIR boundary. If the electric field lines are diffusedand irregular with much fringing, the boundary will also be defused andirregular. Thus it is desirable to confine and direct the electric fieldlines so that the boundary is as nearly a sharply defined flat plane aspossible. FIG. 16 shows a preferred embodiment of the present inventionin which the flatness of the TIR boundary is enhanced.

In the embodiment shown in FIG. 16, the thickness of the matrix layer214, as well as that of the electro-optic material 222 has beenincreased. It should be understood that the relative thicknesses of thelayers shown are for illustration only and are not drawn to scale. Theswitch 210 shown is in the active state, thus charge is applied to thesecond electrode 224 and an electric field has been established in thefirst material portion 226, creating TIR boundary 230. A step region 246has been removed from the second portion 228 by some shaping processsuch as etching including reaction ion etching and plasma etching, laserablation, or use of mechanical processes such as abrasion or cutting, sothat the second material portion 228 has a remaining thickness less thanthe thickness of the first portion 226. A step face 248 is thusestablished as the vertical surface of the first portion 226 above thesecond portion 228 of the electro-optic material 222, this step facebeing created by the removal of second portion 228 material resulting inthe step region 246. The front edge 250 of the second electrode 224 isconfigured to exactly match the profile of the step face 248. In fact,both may be formed simultaneously by first depositing the electrode 224on the electro-optic material 222, and masking the electrode 224 to theextent of the desired material first portion 226. The step region 246 isthen etched or ablated along with the unmasked part of the electrode224, at the same time.

The step region 246 is then filled with some material having a lowdielectric constant (k) and low polarizability (p), which will bereferred to as low k low p material 252. The glass material of thematrix 214 is well suited for use as low k low p material 252, as isair, plastic and many kinds of gases or liquids. The electric fieldlines created when the electrode 224 is charged will not propagate wellin this low k low p step region 246, and will form a sharp boundaryalong the step face 248. This defines the upper portion 254 of the TIRboundary 230 as a flat plane along the step face 248. This flatness anddefinition are extended to all the electric field lines and thusthroughout the lower portion 256 of the TIR boundary 230 which extendsthrough to the substrate 212.

As stated above, the illustration has been drawn without any attempt todepict the relative thicknesses to scale. Representative dimensions are20 microns for the thickness of the PLZT material in the first materialportion 226, a step depth of approximately 7 microns, and thus athickness of 13 microns for the second material portion 228, assumingthat an incident beam is approximately 10 microns in diameter. Thesedimensions are not to be construed as limiting, and much variation ispossible.

It will of course be obvious to one skilled in the art that othervariations and embodiments are possible as well. As mentioned above, itis possible that the two portions 226, 228 are separate components,perhaps composed of different materials. The second portion 228 may evenbe of a non-electro-optic material, in which case, the second electrode224 need not be limited to only the first portion 226, but may extendover both first and second portions 226, 228. Only the first portion 226will then change index of refraction, and the boundary 230 willcorrespond to the physical boundary of the first portion 226 component.The uniformity and quality of reflected image from the TIR boundary 230will then depend on the smoothness of the boundary wall of the firstportion 226, as machined or etched. This type of element may haveadvantages as to ease of manufacture.

For another example of variation, a curved mask could be applied toprovide a curved front edge 250 to the electrode 224 and thus alsoproduce a curved step face 254 and TIR boundary 230. This may have someadvantages in focusing or manipulating the reflected beam 244 profile.For example, the reflected beam can therefore be focused in such a wayas to insure that the beam will be efficiently coupled into the outgoingwaveguide. Thus a separate collimating or focusing element could beeliminated. It is also possible to configure the switch 210 with curvedouter boundaries or other geometric shapes besides the hexagonal shapeshown as the perimeter of the element 218. Perimeter portions 257, asseen in FIG. 16, may be curved or straight, and by providing both acurved perimeter 257 and a curved TIR boundary 230, it is thereforepossible to create a first portion 226 which could be a configured in aconvex-convex lens shape, for one example among many. Of course, manyother combinations of flat and curved surfaces could be used for theperimeter portion 257 and TIR boundary 230 of the first portion 226, andall are contemplated by the present invention.

The switch may also have only one incoming signal channel and twooutgoing signal channels, or more than two incoming and two outgoingsignal channels.

It is also possible for the electrodes to be placed on side surfaces ofthe element rather than top and bottom surfaces. Such a configuration isshown in FIG. 17. The switching element 218 includes side walls 259 towhich the first electrode 213 and second electrode 224 are attached. Asbefore, the first portion 226 is of lesser thickness than the secondportion 228, so that there is a step region 246 formed which serves todirect and confine the TIR boundary 230. An incoming signal beam 240 isshown passing through as if the TIR boundary 230 is inactive, by theblack arrow. Also shown is the reflected beam 244, depicted by a grayarrow, which will result if the TIR boundary 230 is activated. Theelement 218 can be included in a matrix material, which is not shownhere, and included in larger arrays, as will be discussed below.

The optical switches 210 are made to be used in arrays and groups toform N×M matrices for switching signals. FIGS. 18 & 19 illustrate asimple 2×2 cross-connect switch 258 using four optical switches, whichare designated as first switch 260, second switch 262, third switch 264,and fourth switch 266. A first input signal 268 arrives through thefirst input channel 270, and a second input signal 272 arrives throughthe second input channel 274. The incoming signals 268, 272 are eachoptionally passed through collimators 276 and then enter thecross-connect switch 258. A first output channel 278 and a second outputchannel 280 are provided at the output of the cross-connect switch 258.All signals may be routed to the cross-connect switch by signalchannels, as described above, which may be optical fibers, waveguides orfree-space propagation. In FIG. 18, switches 260 and 266 are active, andare represented graphically as active by shading. The switches work aspreviously described to cause TIR of an incoming beam of the appropriatepolarization, assumed vertical, which approaches within an appropriaterange of angles. The first input signal 268 is thus reflected by switch260 and passes through inactive switch 264 to exit through second outputchannel 280. Second input signal 272 also passes through inactive switch264 but is reflected by switch 266 to exit through first output channel280.

FIG. 19 shows the routing of signals when switches 262 and 264 areactive, shown by shading. First input signal 268 passes through inactiveswitch 260, but is reflected by active switch 262 to pass throughinactive switch 266 and finally exit through first output channel 278.Similarly, second input signal 272 is reflected by active switch 264 andexits through second output channel 280.

Of course, it will be obvious that other combinations of active andinactive elements exist, for example, where both switches 260 and 262are inactive so that first input signal 268 will pass in a undeflectedstraight line to arrive at a possible third output channel, not shown.Similarly, if both switches 264 and 266 are inactive, second inputsignal 272 will travel undeflected to a possible fourth output channel,also not shown. Thus the cross-connect switch is not limited to an “N×N”switching matrix, where N=2, for instance, but can be designed to a“N×M” matrix, where, for the combinations discussed immediately above,N=2, and M=4. Also obviously, more switches can be added and more inputand output channels used to increase the number of possible variations.

The optional collimators 276 discussed above are used to collimate thebeam and provide more uniform beam profile within the cross-connectswitch 258. Upon exit from the cross-connect switch 258, there may be afocusing lens, not shown, or other optics to manipulate the size orshape of the beam. The beam exiting from a first cross-connect switchcan be aligned to enter a second cross-connect switch, a fiber optic,waveguide or other optical device, or may be used to excite pixels on adisplay screen.

As alluded to above, the incident signal beam must be of polarizationwhich is parallel to the plane of the beam in order to be reflected byan active TIR boundary. This suggests further possibilities andvariations, for example, where some components of an incoming beam mayhave parallel polarization, and thus are switched by a first element,while other components with polarization orthogonal to the first elementmay pass through unaffected, perhaps to later be switched by a secondswitch having a TIR boundary at the appropriate orientation to nowreflect the signal. It is also possible that larger combinations ofswitches such as the cross connect switch discussed above could bedesigned to only act upon light of a certain polarization, lettingothers pass. Many varieties of signal processing are thus possible. Allsuch variations are contemplated by the present invention.

In addition to the above mentioned examples, various other modificationsand alterations of the inventive device 10 may be made without departingfrom the invention. Accordingly, the above disclosure is not to beconsidered as limiting and the appended claims are to be interpreted asencompassing the true spirit and the entire scope of the invention.

INDUSTRIAL APPLICABILITY

The present device 10 is well suited for application in a wide range offields in which light modulators and high speed light switching devicesare used, such as in high-speed printing, image processing andtelecommunications. The present invention 10 is also especially suitedfor use in flat panel displays and projection television.

Although the basic array structures 10 discussed above are in aone-dimensional line configuration, these may be configured and arrangedto form two-dimensional sheets of large size. Additionally, by use ofthe sol-gel process, they may be used to make a kind of thin flexibledisplay material almost like cloth, which may be used to cover threedimensional forms or perhaps even to make clothing.

The materials presently used in flat panel displays respond very slowlyto changes in display information. This leads to the commonly observedproblem, especially in flat panel displays of laptop computers, that thedisplay of a moving object will leave trails behind, due to the lag inthe response of the display. The present invention, by contrast, istheoretically capable of switching speeds of 100 GHz and more, producingsuch fast response that it is beyond the ability of the human eye toregister individual steps in a display of motion.

Prior art displays also may exhibit the problem of aliasing, or thejagged edges sometimes seen around the outline of a displayed object dueto the comparatively large size of pixels in a digital display. Bycontrast, the elements of the present invention 10 may be made assmaller than 1 μm×1 μm in cross section, each element being capable ofproducing an independent signal. Thus each element is potentially anindependent pixel. The use of the present invention completelyeliminates the problem of aliasing down to the microscopic scale.Indeed, the human eye cannot resolve such small elements. Thus for useon the scale of ordinary unaided human vision, the elements may begrouped into larger pixels, whose overall size can still be small enoughto provide far better image resolution than is presently available.There may also be applications in which microscopic pixel size isadvantageous, such as making microscopic photo masks for microchipmanufacture. The ungrouped pixels of the present invention are uniquelysuited for such uses.

The very small size of the elements allows low driving voltages to beused to produce the necessary electric field density to induce thedesired electro-optic effect. TTL levels may be used with somematerials. The use of TTL level voltages has many significantadvantages. TTL level power supplies have been well developed over manyyears and are commonly available “off the shelf”. Thus power suppliescan be easily obtained for systems that utilize the present invention10, without having to provide a customized power supply. This alsoallows easier introduction of the present invention 10 into equipmentthat uses TTL devices and already has the appropriate power supply inplace.

The present invention 10 also may be designed to utilize sub-TTL levels.It is useful in many applications in which these smaller driver voltagesare supplied.

Prior art light modulators and optical switches that are fabricated on acommon wafer without benefit of any feature to channel the electricfield lines commonly suffer from problems with cross-talk between thechannels. This interferes with image clarity and can corrupt transmitteddata. By contrast, by utilizing the discrete elements of the presentinvention 10, cross-talk between channels is practically eliminated,resulting in cleaner image production and improved accuracy andintegrity of data transmission. This has very many industrialapplications in a wide variety of devices such as printers,telecommunications, and visual displays.

In addition, for telecommunications applications, prior art diode laserswhich have been used, have typically suffered from the problem of“chirping” which is interference which can be produced when the voltagesupplied to a diode laser is rapidly modulated. In contrast, the presentinvention 10 modulates the optical output, rather than the diode laseritself. This greatly reduces interference and can eliminate the problemof chirping. This can be an important advantage for telecommunicationsapplications.

Another feature that makes the present invention 10 especially desirablefor industrial applications is its ease of manufacture and low cost. Itcan be made using existing technology by varying methods such asmicro-machining, laser ablation, selective etching in an electric field,and molding by conventional means or using a sol-gel process. Formicro-machining, the same kinds of micro-saws as are presently used intrimming silicon wafers can be used to form the slots between theprojections.

Another method for manufacturing light modulating arrays 10 is the useof sol-gel processing to create an array of elements that are fixed in aflexible medium. Sol-gel processing is a chemically based, relativelylow temperature method that can produce ceramics and glasses with betterpurity and homogeneity than higher temperature conventional processes.Another of the attractive features of the sol-gel process is thecapability to produce compositions not possible with conventionalmethods.

Thin films of PLZT electro-optic ceramic made with the sol-gel processhave a number of advantages relative to PLZT ceramics prepared frompowders. Large surface areas of thin film can be created which have veryuniform (homogeneous) material structure. Small grain sizes areachievable, in the range of 10's of nm, with much less porosity comparedwith PLZT ceramics prepared from powders. A wide range of film thicknessfrom a few nanometers to a few microns can be produced.

Sol-gel manufacture also easily lends itself to high volume production.It is inexpensive, suitable for large area spatial light modulators orflat panel displays and can utilize micro-machining fabricationprocesses which are standard in the industry. It can be used for bright,ultra high-speed flat panel displays or spatial light modulatorssuitable for computer interconnects and high-speed tele-communicationswith very wide viewing angles which may eventually be used to replacecathode ray tubes.

A light modulating switch 210 as described above creates a totalinternal reflection (TIR) boundary 230 within an electro-optic element218 by providing an electric field in only a first portion 226 of theelectro-optic element. This produces a change in the index of refractionof the material in the first portion 226 so that it is now greater thanthe index of refraction of the non-activated second portion 228.Incident light 240 which approaches at an angle greater than that of thecritical angle for the two indices of the two portions, and which is ofproper polarization orientation, will be reflected into a second path,thus modulating the optical output of the switch 210. The switch canalso be operated at TTL levels and pico-second range switching times.

The operation of the switch is enhanced when the electric field lineswithin the active first portion 226 are narrowly directed, and withminimum fringe effects. In order to decrease fringing, a preferredembodiment of the present invention uses an element 218 which has a stepregion 246 removed from the second portion 228, leaving the firstportion 226 to be of a greater thickness than the second 228. The stepportion is filled with material with a low dielectric constant and lowpolarizability which can be air, glass or plastic. The electric field isthus provided with a sharp boundary at the upper portion 254 of the TIRboundary 230, and this sharp boundary carries into the lower portion 256of the TIR boundary 230. This causes the TIR boundary 230 to be veryflat and sharply defined with very little fringing at the TIR boundaryportion at which the incident beam 240 is reflected. The reflected beam244 thus suffers very little distortion and maintains excellent beamquality throughout modulation or switching.

As alluded to above, TIR will occur only for light of polarizationorientation which is parallel to the plane of the TIR boundary 230.Light of different polarizations can thus be separated into componentsby an active TIR boundary, and this allows additional modes ofmodulation and signal processing that are not available with traditionalelectrical signals.

The optical switch 210 can be easily combined in arrays and N×Mcross-connect switches 258. They will find many uses in optical imagingand telecommunications, especially since they are easy to manufactureand operate.

For the above, and other reasons, it is expected that the device 10 ofthe present invention will have widespread industrial applicability.Therefore, it is expected that the commercial utility of the presentinvention will be extensive and long lasting.

What is claimed is:
 1. An optical switching array comprising: aplurality of optical switches in a planar array, at least one of saidswitches comprising a first non-waveguide section having an index ofrefraction and comprising electro-optic material, a second non-waveguidesection having an index of refraction, said first and second sectionsbeing juxtaposed to form a switchably reflective boundary therebetween,and a pair of spaced electrodes generally parallel to each other andgenerally orthogonal to the plane of the planar array, said electrodeshaving respective surfaces associated with opposite sides of said firstnon-waveguide section to induce an electric field therein and changesaid refractive index; and optical waveguides extending laterally fromsaid optical switches providing optical connection therebetween, whereinsaid plurality of optical switches are laterally disposed across asubstrate, and wherein a light beam entering said at least one opticalswitch (i) is reflected from said switchably reflective boundary whensaid switch is in a first state and the refractive index of the firstsection has a first value, and (ii) is transmitted through saidswitchably reflective boundary when said switch is in a second state andsaid index of the first section has a second value different than thefirst value.
 2. The optical switching array of claim 1, wherein saidelectrodes are formed on sidewalls of said first portion.
 3. The opticalswitch of claim 1, wherein said first and second sections are juxtaposedsuch that said switchably reflective boundary is substantiallyperpendicular to said electrode surfaces.
 4. The optical switching arrayof claim 1, wherein either (i) said second section comprises a materialdifferent in composition than said electro-optic material in said firstsection, or (ii) said second section has a different thickness than saidfirst section.
 5. The optical switch of claim 4, wherein said secondsection comprises a material different in composition than saidelectro-optic material in said first section.
 6. The optical switch ofclaim 4, wherein said second section has a different thickness than saidfirst section.
 7. The optical switch of claim 6, wherein said secondsection has a reduced thickness compared to said first section.
 8. Theoptical switch of claim 1, wherein said electro-optic material compriseslead zirconate titanate doped with lanthanum (PLZT).
 9. An opticalswitching array comprising: a plurality of optical switches in a planararray, at least one of said switches comprising a first non-waveguidesection having an index of refraction and comprising electro-opticmaterial, a second non-waveguide section having an index of refraction,said first and second sections being juxtaposed to form a switchablyreflective boundary therebetween, and a pair of spaced electrodesgenerally parallel to each other and generally orthogonal to the planeof the planar array, said electrodes having respective surfacesassociated with opposite sides of said first non-waveguide section toinduce an electric field therein and change said refractive index;wherein a light beam entering said at least one optical switch (i) isreflected from said switchably reflective boundary when said switch isin a first state and the refractive index of the first section has afirst value, and (ii) is transmitted through said switchably reflectiveboundary when said switch is in a second state and said index of thefirst section has a second value different than the first value, andsaid at least one of said switches has an input for receiving a lightbeam having first and second orthogonal polarizations and said first andsecond sections and electrodes are configured to switch the firstpolarization state and permit a second orthogonal polarization state topass without being switched, and another of said switches has in inputfor receiving said light beam and has first and second sections andelectrodes configured to switch said second orthogonal polarizationstate.
 10. The optical switching array of claim 9, wherein saidplurality of optical switches are laterally disposed across a substrate.11. The optical switching array of claim 10, further comprising opticalwaveguides extending laterally from said optical switches providingoptical connection therebetween.
 12. The optical switching array ofclaim 9, wherein said electrodes are formed on sidewalls of said firstportion.
 13. The optical switch of claim 9, wherein said first andsecond sections are juxtaposed such that said switchably reflectiveboundary is substantially perpendicular to said electrode surfaces. 14.The optical switching array of claim 9, wherein either (i) said secondsection comprises a material different in composition than saidelectro-optic material in said first section, or (ii) said secondsection has a different thickness than said first section.
 15. Theoptical switch of claim 14, wherein said second section comprises amaterial different in composition than said electro-optic material insaid first section.
 16. The optical switch of claim 14, wherein saidsecond section has a different thickness than said first section. 17.The optical switch of claim 16, wherein said second section has areduced thickness compared to said first section.
 18. The optical switchof claim 9, wherein said electro-optic material comprises lead zirconatetitanate doped with lanthanum (PLZT).